Ethernet and USB cables

Regarding Ethernet (presumably to a server or streamer), there are several choices to make,https://www.thecableco.com/cables/usb-cable/galileo-sx-usb.html

• should you use a CAT cable or fiber optic cable
• which CAT cable to use (i.e., 5e, 6, 7, or 8), 
• will a CAT cable that is advertised as being intended for audio systems provide improved performance in some way over a generic CAT cable with the same designation, and then
• if you believe the above, which "audiophile" CAT cable will you purchase

I suggest first reading about the specific differences between CAT cables from sources like this one, or this one.  For transmitting data in a residential setting, virtually any commonly used CAT cable should do the job relative to bandwidth, data rate, and speed, so the differences in their abilities to reject EMI/RFI and crosstalk may be more pertinent features to look at.  You may also want to look at opinions discussing why audio-specific cables may offer improvements over more generic cables, like here or here.

Regarding USB cables, Belkin Gold is one of the best-regarded of the inexpensive OTS options, and many don't see the need to pay for more.  OTOH, many audiophiles report hearing differences between USB cables.  Supra makes a relatively inexpensive USB cable intended for audio that has been favorably reviewed, and prices go up from there with audiophile USB cables ranging in price from several hundred to several thousand dollars.  You may want to search articles discussing USB cable comparisons (like this one) to help you decide where you want to land on the spectrum.

Everybody hears this stuff differently in their own systems and with their own ears.  I settled on a relatively good quality OTS CAT 8 Ethernet cable for my 45-foot run but then switched to fiber, resulting in only a small (negligible?) perceived improvement in sound.  I do seem to perceive differences in USB cables but happily settled on TWL's $330 “Split Power & Data” USB Cable, after trying several.  However, to my ears, none of them changed the basic sonic signature of my system.

It‘s not just the quality of cables, it is also majorly their length. This applies particularly to USB where RFI/EMI incursion is a major problem. For what it‘s worth, I had major benefits from using a short (25cm) Intona Reference cable between server and dac and a short Meicord Ethernet cable between filter and streamer.

Absolutely I had both, my Bricasti is both a very good dac,and streamer the Ethernet  cable has a lower noise floor.
that being said ethernet,or usb the New Wireworld Platinum 8
is a outstanding cable that truly brings out added detail and musicality, highly recommended 1m minimum .

After much ’messing about’ with cables my conclusion was: for long runs optical is best followed by cat 8 down to cat 5. I did not try Hifi quality for this section as the run is 20 meters. For shorter runs I found small differences between cables. There are some very good Hifi quality less expensive cables around. 
For USB there are significant sonic differences, and shorter lengths definitely improves the sound. A friend of mine makes his own and a 20cm cable of his were amongst the best, competing with multi hundred $ cables. In his design he closes off the fifth pin in the usb, the one delivering 5v power - if your DAC does not require any power from the USB, and many don’t, he finds this helps reduce noise from the cable. If your DAC does use the fifth contact oin then this cable won’t work. 
You can actually do this with any usb cable - simply tape over the right hand pin on one end. It’s an easy test and you might hear a difference.